Method of controlling the amount of material in a grinding compartment of a tube mill

ABSTRACT

Controlling the amount of material which is present in a grinding chamber with grinding members of a tubular grinding mill which is divided into a plurality of successively arranged grinding compartments and material reservoir compartments which are in communication through openings which are not large enough to permit the passage of the grinding members from the grinding compartment to the material reservoir compartment by rotating the tubular grinding mill to cause the grinding members to grind the material and to move the ground particles into the material reservoir compartment, and during rotation removing a quantity of material from each material reservoir compartment and delivering a selected portion of the removed quantity to the next adjacent compartment which is downstream thereof. The quantity removed from the material reservoir compartment depends upon the arrangement of the rotatable radially extending scoop which forms a trough or shovel of partial segmental form which is adapted to engage and move through the material during each rotation of the drum to lift a selected quantity of the material upwardly and then to dump it onto a deflector plate so that it moves to the next adjacent downstream compartment. The quantity of material which is removed by one or more scoops is controlled by setting the individual rotative position of the scoop shovels so that they pick up either a greater or lesser quantity of material during each rotation, by adjusting the length of the scoop shovels so that the quantity is varied or by adjusting the amount of material which is either delivered to the next adjacent compartment or backwardly into the material reservoir compartment for recycling.

United States Patent Slegten Apr. 2, 1974 METHOD OF CONTROLLING THE AMOUNT OF MATERIAL IN A GRINDING COMPARTMENT OF A TUBE MILL [76] Inventor: Pierre Arsene Slegten, 158, Avenue du Prince dOrange, Brussels, Belgium [22] Filed: Feb. 15, 1972 [21] Appl. No.: 226,590

Primary Examiner-Granville Custer, Jr. Attorney, Agent, or Firm-McGlew and Tuttle [57] ABSTRACT Controlling the amount of material which is present in a grinding chamber with grinding members of a tubular grinding mill which is divided into a plurality of successively arranged grinding compartments and material reservoir compartments which are in communication through openings which are not large enough to permit the passage of the grinding members from the grinding compartment to the material reservoir compartment by rotating the tubular grinding mill to cause the grinding members to grind the material and to move the ground particles into the material reservoir compartment, and during rotation removing a quantity of material from each material reservoir compartment and delivering a selected portion of the removed quantity to the next adjacent compartment which is downstream thereof. The quantity removed from the material reservoir compartment depends upon the arrangement of the rotatable radially extending scoop which forms a trough or shovel of partial segmental form which is adapted to engage and move through the material during each rotation of the drum to lift a selected quantity of the material upwardly and then to dump it onto a deflector plate so that it moves to the next adjacent downstream compartment. The quantity of material which is removed by one or more scoops is controlled by setting the individual rotative position of the scoop shovels so that they pick up either a greater or lesser quantity of material during each rotation, by adjusting the length of the scoop shovels so that the quantity is varied or by adjusting the amount of material which is either delivered to the next adjacent compartment or backwardly into the material reservoir compartment for recycling.

3 Claims, 7 Drawing Figures I Ill 1111 PATENTEDAPR 2 I974 SHEET 1 0F 2 FIGZ EATENTEU 2 9 4 sum 2 OF 2 FIG.3C

FIGBA FIGBB FIGS METHOD OF CONTROLLING THE AMOUNT OF MATERIAL IN A GRINDING COMPARTMENT OF A TUBE MILL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates in general to a method and apparatus for controlling the amount of material which is ground in various compartments of a grinding mill and, in particular, to a new and useful method of controlling the amount of material in a grinding mill having a plurality of successive grinding compartments arranged therealong which are separated by partitions with two spaced walls defining a reservoir compartment therebetween and to means for selectively removing quantities of material from the reservoir compartment and delivering it to the next adjacent grinding compartment.

2. Description of the Prior Art This invention relates to a method of controlling the amount of material mixed with grinding members in a grinding compartment of a tube mill comprising a partition forming a material reserve chamber and situated downstream of said compartment for performing the method.

Dry or wet grinding of granular materials is generally carried out in tube mills comprising one or more grinding compartments. The amount of material mixed with the grinding members greatly influence the efficiency of the grinding compartment. There must be suff cient material, since otherwise some of the grinding members absorb power without performing useful work and the wear on the grinding elements and protective linings of the tube mill is very intensive. But if there is too much material, the grinding elements lose efficiency and output drops.

Further, for a given output, the amount of material in a grinding compartment determines the residence time of the material in the compartment and the particles size distribution of the final product thus depends on this amount. The ideal amount will, however, vary with grinding conditions and it is therefore important to be able to control the level of material with respect to the grinding members.

Successive grinding compartments are separated by partitions; a partition is also often provided at the downstream end of a single compartment or of the last grinding compartment in order to separate it from the outlet trunnion through which the ground material is discharged.

The partition may be formed by an upstream wall having calibrated apertures for the passage of sufficiently ground material while retaining the grinding elements and insufficiently ground particles, and a downstream wall formed by a substantially solid disc having a central aperture, the upstream and downstream walls together defining a small chamber.

German Pat. No. 177,468 discloses partitions of this kind which are emptied by overflow through the central aperture of the downstream wall; in this arrangement. the chamber of the partition forms a reservoir in which the level of material is determined by the diameter ofthe downstream wall aperture. The level of material in the respective grinding compartments situated upstream of the partition is thus determined by the level in the chamber of the partition and hence also by the diameter of the aperture in the downstream wall.

Thus, there is no control of the level in the grinding compartment with such partitions.

Partitions have also been made with lifting scoops which discharge the material to a deflector which 'directs it towards the aperture of the downstream wall. Generally, the scoops are designed so that they are excessively powerful and consequently the partition chamber has relatively little material in it and the material which passes through its upstream wall can penetrate freely thereto. Various systems have been tried out to control the passage of material through the apertures in the upstream wall of the partition and thus vary the level of material ground in the upstream compartment. In particular, the apertures have been progressively masked from the periphery towards the centre of the partition as in German Pat. No. 420,049 and U.S. Pat. No. 1,787,897. With the partitions according to these patents, the quantity of material in the upstream grinding compartment can be controlled, but in a ball mill there is an appreciable amount of steel scraps originating from the worn grinding members, and such scrap clog in the apertures of the upstream wall and block the aperture masking mechanism, thus making control of the level of material in the upstream compartment impossible.

The invention provides a method of controlling the amount of material mixed with grinding members in a grinding compartment of a tube mill comprising a partition forming a material reservoir chamber and situated downstream of said compartment, comprising the step of controlling the amount of material mixed with grinding members in the grinding compartment by controlling the level of the material in the material reservoir chamber of the partition downstream of said compartment.

SUMMARY OF THE INVENTION The invention further provides a partition for performing said method, comprising an upstream wall having calibrated apertures, a downstream wall in the form of a substantially solid disc having a central discharge aperture, the upstream and downstream walls defining a material reservoir chamber into which the material is driven by rotation of the mill, and from there pours down on a deflector which directs material from the reservoir chamber towards the discharge aperture, and control means adapted to alter the level of the material in the material reservoir chamber.

Accordingly, it is an object of the invention to provide a method of controlling the amount of material which is present with grinding members in a tubular grinding mill which is divided into a plurality of successively arranged grinding compartments and reservoir compartments which communicate with the grinding compartments through perforated walls having openings of a size to permit passage of the grinding material therethrough but not the grinding members and which comprises rotating the grinding mill to grind the material and also to remove a quantity of material from each material reservoir compartment and deliver a selected portion thereof back to the next adjacent grinding compartment or to return a portion to the material reservoir compartment for recycling.

A further object of the invention is to provide a grinding device for grinding material with grinding members which comprises a tubular member having a plurality of grinding compartments therein extending along the length thereof and with partitions separating adjacent compartments having an upstream wall with a passage means to permit the passage of the grinding material therethrough but not the grinding members and a downstream wall having a central discharge passage for delivering material to the next adjacent grinding compartment but, wherein the space between the walls defines a material reservoir for holding a quantity of material to be ground and wherein the partition carries a plurality of scoops which extend radially so that they dip into the material during the rotation of the tubular member and entrain a selected quantity thereof for dumping through the central discharge of the downstream wall or for returning a portion thereof to the reservoir compartment.

A further object of the invention is to provide a grinding machine which is simple in design, rugged in construction and economical to manufacture.

For an understanding of the principles of the invention,,reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a vertical section through the mill;

FIG. 2 is a view on an enlarged scale of part of FIG.

FIGS. 3A to 3C are sections on the line Ill-III in FIG. 1 showing a scoop in 'variousangular positions,

FIG. 4 is a sectional view of a modification of scoop design; and

FIG. 5 is a plan view of the guideway shown in FIG. 1.

GENERAL DESCRIPTION OF THE PREFERRED EMBODIMENT mill by welding, which frames l0, are provided with wide apertures 11. The partitions 8 and 9 have an upstream wall 12 and a downstream wall 13, the walls 12 of both partitions and the wall 13 of the partition 8 being made from a thick material having high resistance to the wear of the grinding members and formed by detachable segments bolted to the frames 10 to allow ready replacement of the segments. The wall 13 of the partition 9 is not subject to the wear of the grinding elements and is made of sheet metal. The walls 12 are formed with calibrated apertures 14 registering with the apertures 11 and allowing the passage of sufficiently ground material while retaining the grinding members and insufficiently ground particles. At the centre of each wall 12 is a grid 15 with apertures just narrow enough to retain the grinding members, this grid allowing the mill ventilating air to pass through the mill. When the grinding is in a wet process, there is no ventilation and therefore the grid 15 is not required. Each wall 13 is in the form ofa solid disc having a central aperture 16. The walls l2 and 13 define a small chamber 17 equiped with lifting scoops 18. This chamber 17 has no grinding members and forms a material reservoir.

The scoops can rotate about their longitudinal axis. As shown in FIG. 2, each scoop l8 bears, on the mill axis side, in a conical seat 19 in a casing 20, which is for example cylindrical or polygonal, and is part of the frame 10, the casing 20 is formed with a circular aperture 21 at each scoop. Outwardly of the part adjacent the casing 20, the scoops 18 form a semi-cylindrical trough. At the end remote from the seat 19, a shaft 22 is secured by a bolt 31 to the scoop and this shaft passes through the barrel 1 via a packing 23. A bearing 24 is secured to the barrel 1 and supports the shaft 22. A spring 25 presses the scoop into the conical seat 19, takes up the wear, and holds the scoop in the selected position. The shaft 22 is controlled by lever 26 carrying a roller 27.

Outside the mill, in the plane of each partition is a guide track 28 which is fixed to the outer race tubes 33 v (FIG. 5) of two linear ball bearings. Inner race axles 34 of the ball bearings are fixed in two cheeks 35 which are parts of a base plate 36 connected to the ground. A hydraulic jack 37, parallel to axles 34, is attached by its head to a support 38 secured to one of the cheeks 35 and by its piston-rod end to the guide track 28. The guide track base plate is situated in such a way that the jack and linear ball bearings are parallel to the mill axis and during the rotation of the mill, the rollers 27 pass through the guide track 28. The guide track may be moved, parallel to the mill axis, on the linear ball bearings, the guide track displacement being operated by the hydraulic jack 37. The guide track 28 has a flared inlet on the side where the rollers 27 enter, during the rotation of the mill, so that the rollers penetrate therein, irrespective of the respective positions of the track and rollers. The guide track 28 has an outlet, the width of which is reduced substantially to the diameter of the rollers 27 so that the latter occupy a defined position when they leave the track 28.

On rotation of the mill, the rollers 27 thus enter the track 28 and are then guided and compelled to move towards the reduced-width outlet of the track. This guidance entails re-positioning of the roller 27 of each scoop on leaving the guide track 28 when the latter has been moved from the previous passage of the same roller 27 and this re-positioning of the roller 27 entails rotation of the lever 26 and of the shaft 22 of the scoop, and hence rotation of the latter.

FIGS. 3A to 3C show three different positions of the scoop 18. In FIG. 3A the scoop is shown in the maxi mum open position, in FIG. 33 it is in the intermediate open position and in FIG. 3C the closed position. Dur ing rotation of the mill, the scoops 18 pass into the material reservoir formed by the chamber 17, the material is lifted and drops towards the centre of the mill as the scoops 18 pass above the mill axis. The material passes through the casing 20 via the apertures 21 and is discharged onto a deflector, for example a frusto-conical member 29 (see FIG. 1), the minor base of which faces the outlet, and which projects the material towards the outlet via the downstream wall discharge aperture 16. The frusto-conical member 29 carries separating fins 30 which prevent the material from turning and falling back into the partition chamber 17. The minor base of the frusto-conical member 29 which is a part of frame 10 is open to allow the passage of air which has passed through the grid 15. From the partition 8, the material passes into the compartment 5 and from the partition 9 into the outlet trunnion.

The useful section of the scoops 18 is of course larger in the position shown in FIG. 3A than in the position shown in FIG. 38 while in the position shown in FIG. 3C it is practically zero. Assuming that the mill is in a state of equilibrium for an amount of material Q passing through the mill and the scoops 18 are in the position shown in FIG. 38, a level of material has formed in the reservoir 17 corresponding to a length I (see FIG. 1) of which the scoops dive into the material reservoir such that with the useful scoop section of FIG. 3B the scoops deliver a quantity of material equivalent to Q. Passing from the position of FIG. 3B to FIG. 3A, the useful section of the scoops increases, the level of material in the chamber 17 drops and equilibrium will be established for a smaller diving length l of the scoops. Conversely, if the useful section is reduced by turning the scoops towards the position of FIG. 3C, the level in chamber 17 rises. By orienting the scoops suitably, the level of material in the chamber 17 can thus be' adjusted. The material in this chamber 17 is a medium which withstands the passage of material through the apertures 14 of the upstream wall of this chamber and hence, by controlling the level in the chamber, the level of material in the grinding compartment immediately upstream can be adjusted. For throughputs Q it is therefore possible to obtain different levels of material in the compartments 4 and 5 and when levels have been found which give optimum grinding efficiency it is possible to maintain them for outputs Q Q etc... different from Q by changing the useful volume of the scoops 18. With conventional partitions, on the other hand, the useful volume of the scoops being non-adjustable, each change of throughput is equivalent to a variation in the level of material in the chambers 17 and hence in the upstream grinding compartments. The output of a mill varying from 1 to more than 3 depending upon the qualities produced, it follows that there will be considerable differences in level and losses in efficiency.

The positioning of the guide track 28 may be made dependent on the feeding of material into the mill so that the useful volume of the scoops 18 is automatically corrected when the rate of feed of the mill is changed.

As shown in FIG. 4, the useful volume of the scoops may also be modified by radially shifting a movable portions 18 of the scoop 18a having a variable length. This movable portion 18 is, for example, held by a stud 32 sliding in a slot in the fixed part of the scoop and by a shaft 22 extending through the cylindrical barrel 1, the shaft being provided with means for locking it in the required position.

What I claim is:

1. In a tube grinding mill, a partition extending transversely therein downstream of one grinding compartment, said partition including an upstream wall with passage apertures of a size to permit passage of the ground material of a predetermined size therethrough but not the grinding members and having spaced axially from said upstream wall a downstream wall with a central discharge passage, the space between said upstream and downstream walls defining a ground material reservoir, said reservoir comprising scoops, the rotation of said tube mill causing said scoops to pick up material from the reservoir, lift said material above mill axis and dump it from there on a central deflector which diverts material through the discharge passage of the downstream wall, said scoops comprising a member in semi-cylindrical form, said semi-cylindrical member being supported by a rotatable shaft with means for rotating said shaft, the material holding volume of said semi-cylindrical member being adjustable in rotating its supporting shaft.

2. A partition, according to claim 1, wherein said means for rotating said shaft includes a bearing for holding said shaft passing through said tube mill, the end of said shaft external to the tube mill having a lever connected thereto which has a follower member, said follower member being engaged with a movable guideway adjacent said tube mill for guiding said follower to rotate said shaft during rotation of the tube mill.

3. In a tube grinding mill, a partition extending transversely therein downstream of one grinding compartment, said partition including an upstream wall with passage apertures of a size to permit passage of the ground material of a predetermined size therethrough but not the grinding members and having spaced axially from said upstream wall a downstream wall with a central discharge passage, the space between said upstream and downstream walls defining a ground material reservoir, said reservoir comprising scoops, the rotation of said tube mill causing said scoops to pick up material from the reservoir, lift said material above mill axis and dump it from there on a central deflector which diverts material through the discharge passage of the downstream wall, said scoops comprising two telescopic portions, said portions being extensible and retractable for varying the material holding volume of said scoops, one of said telescopic portions including means to permit the setting thereof relative to the other of said telescopic portions. 

1. In a tube grinding mill, a partition extending transversely therein downstream of one grinding compartment, said partition including an upstream wall with passage apertures of a size to permit passage of the ground material of a predetermined size therethrough but not the grinding members and having spaced axially from said upstream wall a downstream wall with a central discharge passage, the space between said upstream and downstream walls defining a ground material reservoir, said reservoir comprising scoops, the rotation of said tube mill causing said scoops to pick up material from the reservoir, lift said material above mill axis and dump it from there on a central deflector which diverts material through the discharge passage of the downstream wall, said scoops comprising a member in semicylindrical form, said semi-cylindrical member being supported by a rotatable shaft with means for rotating said shaft, the material holding volume of said semi-cylindrical member being adjustable in rotating its supporting shaft.
 2. A partition, according to claim 1, wherein said means for rotating said shaft includes a bearing for holding said shaft passing through said tube mill, the end of said shaft external to the tube mill having a lever connected thereto which has a follower member, said follower member being engaged with a movable guideway adjacent said tube mill for guiding said follower to rotate said shaft during rotation of the tube mill.
 3. In a tube grinding mill, a partition extending transversely therein downstream of one grinding compartment, said partition including an upstream wall with passage apertures of a size to permit passage of the ground material of a predetermined size therethrough but not the grinding members and having spaced axially from said upstream wall a downstream wall with a central discharge passage, the space between said upstream and downstream walls defining a ground material reservoir, said reservoir comprising scoops, the rotation of said tube mill causing said scoops to pick up material from the reservoir, lift said material above mill axis and dump it from there on a central deflector which diverts material through the discharge passage of the downstream wall, said scoops comprising two telescopic portions, said portions being extensible and retractable for varying the material holding volume of said scoops, one of said telescopic portions including means to permit the setting thereof relative to the other of said telescopic portions. 